#include <iostream>
#include <algorithm>
using namespace std;
const int N = 1e5 + 10;
typedef long long LL;
LL a[N];
int l, n, m;

int calc(LL len)
{
    // 模拟跳跃过程
    int ret = 0;
    for(int i = 0;i <= n + 1;)
    {
        int j = i + 1;
        while(j <= n + 1 && a[j] - a[i] < len) j++;
        ret += j - i - 1;
        i = j;
    }
    return ret;
}

int main()
{
    cin >> l >> n >> m;
    for(int i = 1;i <= n;i++) cin >> a[i];

    a[n + 1] = l;

    int r = l, l = 1;
    while(l < r)
    {
        LL mid = l + (r - l + 1) / 2;
        if(calc(mid) <= m) l = mid;
        else r = mid - 1;
    }

    cout << l << endl;
    return 0;
}